Magnesium alloy and method of making the same

ABSTRACT

A magnesium alloy includes about 7.2 to about 7.8 wt % aluminum, about 0.45 wt % to about 0.90 wt % zinc, about 0.17 wt % to about 0.40 wt % manganese, about 0.30 wt % to about 1.5 wt % rare earth elements, about 0.00050 wt % to about 0.0015 wt % beryllium, and the rest being magnesium and unavoidable impurities. A method of making the magnesium alloy is further provided.

BACKGROUND

1. Technical Field

The present disclosure relates to magnesium alloys, particularly to a magnesium alloy having good mechanical properties and a method of making the same.

2. Description of the Related Art

Magnesium alloys have low density, high mechanical strength, high thermal conductivity, high electrical conductivity, good electromagnetic interference shielding property, and good machining property, and have been widely used in the aerospace, automotive industries and consumer electronic devices. Due to consumer demand of thinner electronic devices, structure strength of the consumer electronic device cannot meet product needs when employing general-grade magnesium alloys.

Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with reference to the following drawings.

FIG. 1 is a flowchart of a method of making a magnesium alloy of an illustrated embodiment.

FIG. 2 is a table presenting the results of the mechanical properties of the magnesium alloy of an example 1.

FIG. 3 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 2.

FIG. 4 is a table presenting the results of the mechanical properties of the magnesium alloy from example 3.

FIG. 5 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 4.

FIG. 6 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 5.

FIG. 7 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 6.

FIG. 8 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 7.

FIG. 9 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 8.

FIG. 10 is a table presenting the results of the mechanical properties of the magnesium alloy from an example 9.

FIG. 11 is a table presenting the results of the mechanical properties of the AZ91D magnesium alloy.

FIG. 12 is a table presenting the results of the drawing load of a camera housing made of the magnesium alloy from the example 5.

FIG. 13 is a table presenting the results of the drawing load of a camera housing made of the AZ91D magnesium alloy.

FIG. 14 is a table presenting the results of etching weight per square centimeter when dipping the magnesium alloy from the example 5 and the AZ91D magnesium alloy in salt water.

DETAILED DESCRIPTION

An embodiment of a magnesium alloy contains the following: about 7.2 weight (wt) % to about 7.8 wt % aluminum (Al), about 0.45 wt % to about 0.90 wt % zinc (Zn), about 0.17 wt % to about 0.40 wt % manganese (Mn), about 0.30 wt % to about 1.5 wt % rare earth elements (RE), about 0.0005 wt % to about 0.0015 wt % beryllium (Be), and the rest being magnesium (Mg) and unavoidable impurities. RE is preferably one or more materials selected from the group consisting of cerium (Ce), lanthanum (La), praseodymium (Pr), neodymium (Nd), yttrium (Y) and any suitable combination thereof. The preferred range of RE is about 0.90 wt % to about 1.2 wt %. In the illustrated embodiment, RE contains the combination of La and Ce. Preferably, the weight ratio (in percent) of Ce to RE is about 65%, and the weight ratio (in percent) of La to RE is about 35%.

Referring to FIG. 1, a method of making the above-described magnesium alloy of the embodiment includes following steps.

In a first step S101, raw materials are provided. The raw materials contains: about 7.2 wt % to about 7.8 wt % Al, about 0.45 wt % to about 0.90 wt % Zn, about 0.17 wt % to about 0.40 wt % Mn, about 0.30 wt % to about 1.5 wt % RE, about 0.0005 wt % to about 0.0015 wt % Be, and the rest being Mg and impurities. Preferably, in the illustrated embodiment, the Al (composition) includes pure Al and an Al—Be inter-alloy, the Zn includes pure Zn, the Mn includes anhydrous manganese dichloride (MnCl₂), the RE includes a Mg—RE inter-alloy, the Be includes an Al—Be inter-alloy, and the Mg includes pure Mg and a Mg—RE inter-alloy. The RE (composition) can be one or more materials selected from the group consisting of Ce, La, Pr, Nd, Y, and any suitable combination thereof.

In a second step S102, a raw Mg—Al—Zn alloy is formed. The pure Mg is melted, and the pure Al, the pure Zn, and the anhydrous MnCl₂ are added into the melted Mg at a temperature of about 700 degrees Celsius, such that the raw Mg—Al—Zn alloy is obtained.

In a third step S103, a refined Mg—Al—Zn alloy is formed. A refining flux is added into the above-mentioned raw Mg—Al—Zn alloy to remove impurities at a temperature of about 720 degrees Celsius, and the temperature is maintained for 0.5 hours to obtain the refined Mg—Al—Zn alloy.

In a fourth step S 104, a Mg—Al—Zn—RE alloy is formed. The Mg—RE inter-alloy and the Al—Be inter-alloy are added into the refined Mg—Al—Zn alloy, and a mixture of the above-mentioned alloys is stirred for about 0.5 hours, cooled to a temperature of about 670 degrees Celsius, and then casted to obtain the Mg—Al—Zn—RE alloy. It is understood that the pure RE and the pure Be may be added instead of the Mg—RE inter-alloy and the Al—Be inter-alloy.

In the illustrated embodiment, the RE contains the combination of La and Ce. Preferably, the weight ratio (in percent) of Ce to RE is about 65%, and the weight ratio (in percent) of La to RE is about 35%. It is understood that the RE can be one or more materials selected from the group consisting of Ce, La, Pr, Nd, Y, and any suitable combination thereof.

An example 1 of the method of making the magnesium alloy of the embodiment is as follows.

In a first step, a plurality of raw materials are provided. The raw materials contain about 7.2 wt % Al, about 0.68 wt % Zn, about 0.28 wt % Mn, about 0.30 wt % RE, about 0.0010 wt % Be, and the rest being Mg and unavoidable impurities. The Al (composition) includes pure Al and Al-Be inter-alloy, the Zn includes pure Zn, the Mn includes anhydrous manganese dichloride (MnCl₂), the RE includes a Mg-RE inter-alloy, the Be includes an Al—Be inter-alloy, and the Mg includes pure Mg and a Mg—Ce—La inter-alloy. The RE contains the combination of Ce and La. The weight ratio (in percent) of Ce to RE is about 65%, and the weight ratio (in percent) of La to RE is about 35%. The total weight ratio (in percent) of Ce and La in the Mg—RE inter-alloy is about 20%. The weight ratio (in percent) of Be in the Al—Be inter-alloy is about 1%.

In a second step, a raw Mg—Al—Zn alloy is formed. The pure Mg is melted, and the pure Al, the pure Zn, and the anhydrous MnCl₂ are added into the melted Mg at a temperature of about 700 degrees Celsius, such that the raw Mg—Al—Zn alloy is obtained.

In a third step, a refined Mg—Al—Zn alloy is formed. A refining flux is added into the above-mentioned raw Mg—Al—Zn alloy to remove impurities at a temperature of about 720 degrees Celsius, and the temperature is maintained for about 0.5 hours to obtain the refined Mg—Al—Zn alloy.

In a fourth step, a Mg—Al—Zn-RE alloy is formed. The Mg-RE inter-alloy and the Al—Be inter-alloy are added into the refined Mg—Al—Zn alloy, and a mixture of the above-mentioned alloys is stirred for about 0.5 hours, cooled to a temperature of about 670 degrees Celsius, and then casted to obtain the Mg—Al—Zn-RE alloy.

An example 2 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 2, in the first step, the raw materials contain about 7.5 wt % Al. Meanwhile, the Zn, Mn, RE, and Be have the same respective weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 3 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 3, in the first step, the raw materials contain about 7.8 wt % Al. Meanwhile, the Zn, Mn, RE, and Be have the same respective weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 4 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 4, in the first step, the raw materials contain about 1.0 wt % RE. Meanwhile, the Al, Zn, Mn, and Be have the same weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 5 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 5, in the first step, the raw materials contain about 7.5 wt % Al, and about 1.0 wt % RE. In addition, the Zn, Mn, and Be have the same weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 6 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 6, in the first step, the raw materials contain about 7.8 wt % Al, and about 1.0 wt % RE. The Zn, Mn, and Be have the same weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 7 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 7, in the first step, the raw materials contain about 1.5 wt % RE. The Al, Zn, Mn, and Be have the same weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 8 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 8, in the first step, the raw materials contain about 7.5 wt % Al, and about 1.5 wt %. RE. The Zn, Mn, and Be have the same weight % or ratios as for the example 1, and the rest is Mg and unavoidable impurities.

An example 9 of the method of making the magnesium alloy of the embodiment is similar to the example 1 of the method of making the magnesium alloy of the embodiment. However, for the example 9, in the first step, the raw materials contain about 7.8 wt % Al, and about 1.5 wt %. RE. The Zn, Mn, and Be have the same weight % or ratio as for the example 1, and the rest is Mg and unavoidable impurities.

The tensile strength, the percentage of elongation, and the yield strength of the magnesium alloy samples of the above examples and those of the AZ91D magnesium alloy sample were tested according to ASTM E8M-04 Standard Test Methods for Tension Testing of Metallic Materials. The impact toughness of the magnesium alloy samples of the above examples and those of the AZ91D magnesium alloy sample were tested according to ASTM E3-04 Standard Test Methods for Notched Bar Impact Testing of Metallic Materials. The results are shown in FIGS. 2 through 11. The average values of the mechanical parameters of 30 samples are shown in Table 1.

TABLE 1 tensile impact strength percentage of yield strength toughness sample (MPa) elongation (%) (MPa) (J/cm²) example 1 245 8.2 139 8.5 example 2 239 7.2 139 6.8 example 3 233 6 140 7.2 example 4 260 10 142 9.5 example 5 260 9.4 141 8.6 example 6 255 7.8 146 7.7 example 7 255 10.2 136 9.9 example 8 258 9.5 142 9.1 example 9 263 8.3 149 8.7 AZ91D 214 3.1 149 5.4

Compared to the AZ91D magnesium alloy, the magnesium alloys of the embodiment of instant disclosure have a relatively low Al content, and contains RE element. As shown in FIGS. 2 through 11, and Table 1, the magnesium alloys of the respective examples have relatively excellent mechanical properties, especially the percentage of elongation, the impact toughness and the tensile strength. The lower the Al content is, the greater the tensile strength are, as well as the percentage of elongation, and the impact toughness; however, the greater the melting point of the magnesium alloy is, the castability of the magnesium alloy and the service life of the mold are thereby more negatively affected. Therefore, the Al content is preferably about 7.5 wt %. The higher the RE content is, the greater the tensile strength are, as well as the percentage of elongation, and the impact toughness; however, the higher the cost of the magnesium alloy becomes. Therefore, the RE content is preferably about 1.0 wt %.

To further test the mechanical property of a consumer electronic device made of the magnesium alloy from the above examples for the embodiment, the drawing loads of camera housings made of the magnesium alloy from the example 5 and the AZ91D magnesium alloy were tested on a universal testing machine. A thickness of a drawing position is about 1.16 millimeters (mm) The test results are shown in FIGS. 12 and 13. The average values of the drawing load of 100 camera housing samples are shown in Table 2.

TABLE 2 sample average drawing load (N) example 5 386 AZ91D 291

As shown in FIGS. 12 and 13, and Table 2, compared to the camera housing made of the AZ91D magnesium alloy, the camera housing made of the magnesium alloy of the example 5 has a relatively better drawing load and structural strength, which are consistent with and corresponding to the test results of the mechanical properties of the magnesium alloys.

The corrosion resistance of the magnesium alloys of the embodiments and the AZ91D magnesium alloy were tested by the salt spray test, according to the standard JIS Z 2371. The test results are shown in Table 3. In addition, the corrosion resistances of the magnesium alloys of the examples and the AZ91D magnesium alloy were further tested by a salt water dipping method. The salt water dipping method includes steps as follows: a magnesium alloy sample having a length of about 20 mm, a width of about 20 mm, and a thickness of about 5 mm is dipped into about 5 wt % sodium chloride solution for about 96 hours; the volume of hydrogen released during the time period is tested; and the corrosion weight per square centimeters of the sample is calculated according to the hydrogen volume. The test results are shown in FIG. 14.

TABLE 3 sample sample 1 sample 2 sample 3 average example 1 8 7 7 7.3 example 2 8 7 7 7.3 example 3 7 7 7 7 example 4 8 7 7 7.3 example 5 9 8 8 8.3 example 6 8 8 8 8 example 7 7 8 7 7.3 example 8 8 8 7 7.6 example 9 8 8 7 7.7 AZ91D 7 7 8 7.3

As shown in Table 3 and FIG. 14, the corrosion resistance of the magnesium alloy of the examples of the embodiment of instant disclosure is greater than that of the AZ91D magnesium alloy. Because the combining force between RE element and oxygen is greater than that between magnesium and oxygen, during the melting process, RE can combine with oxygen to form RE oxide, such that the oxygen impurities can be removed. In addition, during the melting process, magnesium is easily reacted with water vapor to release hydrogen gas, such that gas hole can be caused in magnesium alloy casting, which negatively affects the corrosion resistance of the magnesium alloy. RE can react with hydrogen, thereby preventing the gas hole from forming, and thus the corrosion resistance can be improved.

Because of good mechanical properties and corrosion resistance, the magnesium alloys of the examples of the embodiment of instant disclosure are especially suitably or properly used in the manufacture of housings of consumer electronic devices.

It is to be understood, however, that even through numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A magnesium alloy containing: about 7.2 wt % to about 7.8 wt % aluminum, about 0.45 wt % to about 0.90 wt % zinc, about 0.17 wt % to about 0.40 wt % manganese, about 0.30 wt % to about 1.5 wt % rare earth elements, about 0.00050 wt % to about 0.0015 wt % beryllium, and the rest being magnesium and unavoidable impurities.
 2. The magnesium alloy of claim 1, wherein the aluminum is about 7.5 wt % aluminum.
 3. The magnesium alloy of claim 1, wherein the rare earth element is about 1.0 wt % rare earth element.
 4. The magnesium alloy of claim 1, wherein the rare earth element is selected from the group consisting of cerium, lanthanum, praseodymium, neodymium, yttrium, and combinations thereof.
 5. The magnesium alloy of claim 4, wherein the rare earth element is the combination of cerium and lanthanum.
 6. The magnesium alloy of claim 5, wherein the weight ratio of cerium to rare earth element is about 65%, and the weight ratio of lanthanum to rare earth element is about 35%. 7-20. (canceled) 